Social media posts by pro-Russian insurgents - most of them hastily removed - suggest the rebels thought they had shot down a Ukrainian army plane before realising in horror that it was in fact a packed Malaysian airliner.

The Twitter and blog messages were immediately publicised by top Kiev officials in their furious information war with the Kremlin in the aftermath of the crash of Malaysian Airlines flight MH17.

Meanwhile, a YouTube channel purportedly run by the Security Service of Ukraine has released audio of what it claims are pro-Russian militants taking responsibility for shooting down flight MH17.

The audio’s veracity has not yet been confirmed, but the Security Service of Ukraine’s official website has published a link to the YouTube video.

Confirmation of separatist fighters killing passengers and crew on a flight from Amsterdam to Kuala Lumpur would further complicate Russian President Vladimir Putin's efforts to paint their uprising as a fight for self-determination.

An armed pro-Russian separatist stands at the site of the Malaysia Airlines Boeing 777 plane crash. Photo: Reuters

Russia's state media avoided any mention of the controversial posts and instead reported militia leaders' later charges that the Ukrainian air force had shot down the Boeing 777 liner instead.

'We downed an An-26'

The rebels first claimed to have downed at least one Ukrainian army plane over the strife-torn eastern rustbelt on late Thursday afternoon.

Emergencies Ministry member works at putting out a fire at the crash site. Photo: Reuters

The VK social networking page of Igor Strelkov - "defence minister" of the self-proclaimed Donetsk People's Republic - first announced: "We just downed an An-26 near (the town of) Torez."

"And here is a video confirming that a 'bird fell'," said the post.

The website then provides a link identical to that published by Ukrainian media in reports about the Malaysia Airlines jet.

Emergencies Ministry members at the crash site. Photo: Reuters

The video shows locals referring to the same coal mine in the region mentioned by Strelkov.

The strongly pro-Kiev Ukrainska Pravda news site later posted an audio recording of what it claimed were the intercepted field communications between rebels and a Russian agent discussing the downing.

"We just downed a plane," a rebel the recording identifies as Bes (Demon) tells an alleged Russian military intelligency officer.

Major: Yes. One belonging to a student from Indonesia. From Thompson University.

'We have seized missiles'

The VK post was soon removed - but not before its screen grab was reportedly captured and distributed in an English-language press release by the military headquarters of Kiev's eastern campaign.

The comments attributed to Strelkov did not identify what missile was used to down the craft at what Kiev said was an altitude of 10,000 metres (33,000 feet).

But a message on the official Twitter account of the Donetsk People's Republic had announced hours earlier that insurgents had seized a series of Russian-made Buk systems capable of soaring to that height.

"@dnrpress: self-propelled Buk surface-to-air missile systems have been seized by the DNR from (Ukrainian) surface-to-air missile regiment A1402," said the post.

That tweet was later deleted as well.

Putin says Kiev responsible

Ukraine's pro-Western President Petro Poroshenko quickly called the incident a "terrorist act" and said he "could not exclude" that the plane was shot down by the insurgents.

But Putin said the incident would never have happened had Poroshenko not ripped up a brief truce agreement and "resumed military activities in southeastern Ukraine".

Both separatist leaders and Russian defence officials also took pains to implicate Poroshenko's forces and erase all memories of the insurgents' initial pronouncements about downing a Ukrainian transport plane.

Rebel Donetsk prime minister Oleksandr Borodai told Russian media that his units did not have equipment capable of reaching the cruising altitude of a Boeing.

Borodai said it was "technically impossible" for the pro-Russian gunmen to have launched such a high-altitude strike.

And the Russian defence ministry argued that it was far more likely for the Ukrainian military to have fired the Buk missile.

"Statements by Kiev officials that such systems ... were not used in air attacks arouse serious doubts," the Russian defence ministry said in a statement.

18 Jul
Russian President Vladimir Putin on Friday said Ukraine bore responsibility for the downing of a passenger plane in the country's east, saying it would not have happened if Kiev had not resumed a military campaign against separatists.

18 Jul
The prime suspect goes by the name Strelkov — or "shooter". Real name Igor Girkin, the former Russian intelligence officer has shot his own troops for insubordination. He may have just shot down a passenger plane with 298 people on board.

18 Jul
If initial reports are true, the Malaysia Airlines Flight 17 crash is the deadliest incident of a civilian passenger plane being shot down in modern memory. Sadly, there is a long history of passenger craft being prey to overzealous military forces.

18 Jul
The rebels are suspect number 1. But there are other scenarios in the shooting down of Malaysia Airline Flight 17 above eastern Ukraine that will fuel conspiracies in the conflict. None end well.